Carbamic acid 3-(4-benzyloxy-phenyl)-isoxazol-5-ylmethyl ester is an azole derivative having the following formula:

It was filed as Korean Patent Application No. 2010-0016686. This compound has a high protection efficacy for the nerve cell and thus shows a therapeutic effect to such diseases associated with the death of nerve cells or neurodegeneration. However, since it has an extremely low solubility in water, it shows a very low bioavailability when orally administered.
Insoluble drugs show a low solubility and dissolution rate in the gastric juice, body fluids, etc. due to their low solubility in water and thus their absorption through the gastrointestinal tract is inhibited to give a low bioavailability when they are orally administered. Thus, various approaches have been tried to improve the solubility or absorptivity of the insoluble drugs. Examples thereof include converting the crystalline compound to its amorphous form, giving the physical change of increasing the surface area through micronization, or developing an emulsion or a microemulsion using a surfactant or a suitable solvent to increase the solubility and absorptivity. Since the amorphous form has a higher water solubility—as much as 10-1600 times or more than the crystal form—if a compound is converted to an amorphous form, its bioavailability may increase remarkably. However, the amorphous form is highly apt to be recrystallized again to a crystal form having a low free energy with the passage of time and thus has the disadvantage of low storage stability. The approach of increasing surface area through the micronization of particles may be effective in improving the solubility rate of such compounds having a low solubility rate. However, the intrinsic solubility of a compound cannot be changed. Furthermore, the micronization using a mill such as a hammer mill or a jet mill can be applied with some limitation depending on the energy reactivity of the compound. Methods for improving solubility by preparing a microemulsion using a solubilizer such as a surfactant are frequently applied, but the use of a solubilizing agent, organic solvent or surfactant is constrained due to their toxicity. As another method for improving the solubility of insoluble drugs, researches using a solid dispersion have been tried. The solid dispersion is a system wherein the drug particles are dispersed in the water-soluble polymer matrix in the solid phase. It can broaden the surface area of drug particles by reducing their size. Since the drug is converted to an amorphous form during the method of preparing the solid dispersion and thus exists partially or completely in amorphous form, it is effective in terms of increasing the drug solubility and its storage property. Spray-drying and melt-extrusion have been known as methods for preparing the solid dispersion. Spray-drying is a method for preparing the solid dispersion by mixing a drug and a water-soluble polymer with a suitable solvent depending on the characteristics of the drug and the water-soluble polymer, and then spraying the mixture. The spray-drying method has the problem that it is difficult to find a solvent that can dissolve the insoluble drug and the water-soluble polymer together. Particularly, when the drug has a low solubility in the solvent selected, since a large amount of the organic solvent should be used, the method can hardly be applied in commercial production and may cause the problems of solvent recovery and environmental pollution. The melt-extrusion is a method for forming solid dispersion by melting a mixture of drug and water-soluble polymer at the temperature of the melting point of the drug and the glass transition temperature of the polymer mixture or higher to convert the drug into an amorphous form and by extruding it, endowing the polymer with plasticity. The present inventors have found that a solid dispersion of an insoluble compound, whose solubility, bioavailability and physico-chemical stability are remarkably improved, can be effectively prepared by using the melt-extrusion method under specific conditions. They then completed the present invention.